Cook the pasta in salted water until al dente. Mix well creme fraiche with lemon juice and season with salt and pepper. Cut fish into cubes. Wash rocket salad. Add 3 mintues before end of cooking the peas to the pasta and skim off 150 ml cooking water. Strain pasta and peas and drain. Add 150 ml cooking water in a pot, heat and add the diced fish and simmer about 4 minutes. Add creme fraiche, rocket and pasta, mix well, heat and season with salt and pepper.